A photonic crystal is a nanostructure in which the refractive index varies on a periodic basis, and can control wavelengths of light passing through it. A photonic crystal surface light-emitting laser (referred to hereinafter as PCSEL) using a two-dimensional photonic crystal (referred to hereinafter as 2DPC) is proposed as a next-generation semiconductor surface light-emitting element. PCSEL is characterized in that the optical properties thereof are determined by the size and shape of microstructure, independent of materials, and has new properties hard to be achieved by the conventional semiconductor light-emitting elements alone, such as large area and single mode, two-dimensional polarization control, and control of emission angle, leading to a potential to develop a probability of a high-output semiconductor laser.
Practical fabrication of 2DPC employs the wafer bonding technology and has the following problems (1) to (3). (1) It is difficult to produce a large-area 2DPC. Specifically, for example, when wafers to be bonded are warped, when there is dust between wafers, or when wafer surfaces are significantly uneven, these wafers cannot be well bonded to each other. (2) The 2DPC layer includes cavities and the coupling coefficient K is large, which is not suitable for implementation of large area. The reason for it is as follows: in order to distribute light uniformly over the 2DPC layer, it is desirable to set the normalized coupling coefficient KL in in-plane directions relative to the electrode length L in the range of about 1 to 2, but in the case where the 2DPC layer includes cavities, the value of K becomes not less than 1000 cm−1 and the value of L is thus limited to several ten μm. (3) There are defects formed at the interface between the bonded wafers, which leads 10 to drawbacks in lifetime and reliability.
A regrowth type PCSEL using regrowth of crystal is offered as 2DPC fabrication means to solve the above problems, and this has the following advantages. (1) It is easy to fabricate a large-area 2DPC. Namely, the use of regrowth eliminates the need for bonding crystals. (2) When the 2DPC layer is perfectly embedded, the coupling coefficient κ thereof becomes reduced to about 1/10 of the coupling coefficient in the case of the wafers being bonded, which facilitates implementation of large area. (3) The interface of the 2DPC layer is embedded by epitaxial layer, which decreases defects and improves reliability. (4) Since the 2DPC layer includes no cavities, it is excellent in heat radiation and is suitable for increase of power.
From the above-described viewpoints, the regrowth type PCSEL is superior to the bonded type PCSEL, in terms of aiming at practical use of high-output PCSEL.
Patent Literature 1 describes a proposal of embedding hexagonal projections in a semiconductor layer, as photonic crystals without cavities in the regrowth of crystal. In this case, with respect to the principal surfaces of (0001) plane of the projections, the side faces are comprised of (1-100) facets.
Patent Literature 2 describes execution of regrowth embedding in crystal growth of the zinc blende structure using a (111) substrate with a polar plane or a (n11) substrate (preferably, 2≦n≦6) with a semipolar plane, and uses lateral growth as means thereof.